Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B22/00—Buoys
  • B63B22/02—Buoys specially adapted for mooring a vessel
  • B63B22/021—Buoys specially adapted for mooring a vessel and for transferring fluids, e.g. liquids
  • B63B22/023—Buoys specially adapted for mooring a vessel and for transferring fluids, e.g. liquids submerged when not in use
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B27/00—Arrangement of ship-based loading or unloading equipment for cargo or passengers
  • B63B27/24—Arrangement of ship-based loading or unloading equipment for cargo or passengers of pipe-lines

Definitions

• the invention relates to a system for handling a transfer device for transferring fluid loads from a sub sea tension buoy to a vessel on the sea surface.
• FIG. 1 A prior art system for transferring load from a storage tank 1 (located as a separate unit sub sea or integrated into a production platform/vessel) to a tanker 2 on the sea surface is illustrated in figures 1 and 2.
• the load is a hydrocarbon fluid comprising oil, gas and/or other components from the storage tank 1 , flowing to a riser base 3 via the flow line la and further up a main riser 4, through a tension buoy 14 and further through an active transfer device (collectively 13 and 20)
• the active transfer device located on top of the tension buoy 14 comprises a swivel 20 and a gooseneck 13 leading up from a loading riser 10.
• the loading riser 10 may be a flexible riser or hose, which hangs freely down from the swivel/gooseneck on the tension buoy 14 when not in use (i.e. on standby) as shown in figure 2.
• the loading riser 10 is connected to the tanker 2, and the swivel gooseneck 13 is free to swivel in order to keep the tanker 2 downwind from the tension buoy 14 as the wind shifts direction during loading as illustrated in figure 1.
• a pick up system In order to transfer the loading riser 10 from the standby mode (hanging down), to the loading mode (when it is connected to the tanker 2), a pick up system is required.
• a pick up system can be implemented in many ways, but the pick up system associated with the present invention may comprise the following known elements:
• a pick up line 11 runs from the free end of the loading riser 10 (the end valve) to a spring buoy 15 near the level of the tension buoy 14.
• An intermediate pick up line 1 1a runs to a master link 16 some 15 m below the sea surface 5.
• An upper pick up line 1 lb runs from the master link 16 to a marker buoy 17 at the sea surface.
• the present invention may also work with other configurations of a pick up system. Hence the pick up system is not part of the invention.
• the tanker moves close to the marker buoy 17, picks it up and connects it to the tanker's pull in line 18 and so to the master link 16.
• the tanker's pull in line 18 is connected to a winch which is a part of the tanker's tension buoy 19.
• the winch is activated and pulls the pull in line 18 and the pick up line 1 la in towards the tension buoy 19.
• the loading riser 10 end valve follows the pick up line and engages in the tension buoy 19 when the pick up line is pulled in to its end. Transfer of the hydrocarbons can now start.
• the loading riser 10 and the pick up system 11 needs to be disconnected.
• the tanker's pull in line 18 is paid out until the master link 16 appears in the connection device on the tanker's tension buoy 19.
• the loading riser 10 is again in a vertical position.
• the upper pick up line l ib and the marker buoy 17 are then connected to the master link 16 and the pull in line 18 is disconnected.
• the upper pick up in line l ib and the marker buoy 17 are again an integral part of the pick up system 11. They are then thrown overboard and the tanker leaves the site. The system is now again in the standby mode.
• the system described above is a very simple pickup system. It works well during loading and disconnection operations, but it runs a significant risk of becoming entangled in the swivel/gooseneck details 20 and 13 as well as wrapping itself around the rigid riser 4 during standby operation. If this occurs, the pick up process will become impossible without the aid of a remotely controlled vehicle to disentangle the system. This is why the industry has in the past employed much more elaborate and expensive pick up systems, where this particular risk is eliminated. Such systems become exceedingly expensive as well as cumbersome from an operational point of view in deep water, and finally at some depth they are no longer a feasible alternative.
• An objective of the present invention is to prevent the pickup line from becoming entangled as well as wrapped around the rigid riser.
• the invention enables the use of a simple pick up system, such as that described above. As a result water depth is no longer a critical parameter for loading systems like the one described above (or for similar systems).
• the mechanism of the invention is a position limiting device 21, for example in the form of a wheel (with a diameter significantly larger than that of the tension buoy), located above the swivel/gooseneck active transfer device.
• the wheel centre is in the centre line for the vertical swivel motion and it rotates with the swivel.
• the wheel circumference is equipped with devices that "catch” the pick up line if it comes in touch with it.
• the position limiting device 21 may also be denoted a "catching wheel” or a "catchwheel”.
• the invention provides a system for handling a transfer device for transferring fluid loads from a subsea tension buoy to a vessel on the sea surface, comprising:
• connection device for connection of the transfer device to the tension buoy, where the transfer device is hanging from the connection device when no fluid loads is being transferred;
• a pickup line comprising a first end connected to the transfer device and a second end available at the sea surface;
• a swiveling device connected between the connection device and the tension buoy for rotation of the connection device in relation to the tension buoy; a position limiting device fixed above the connection device, for limiting the position of the pickup line in relation to the tension buoy; where the pickup line is provided in a tensioned state at least up to the level of the position limiting device.
• the swiveling device is provided for free rotation of the connection device substantially in a horizontal plane according to influence from the sea.
• the position limiting device comprises a catching device for catching and holding the pickup line.
• the catching device comprises a releasing mechanism for releasing the pickup line from the catching device.
• the releasing mechanism is provided for release of the pickup line when a traction force in the pickup line reaches a predetermined limit.
• the catching device comprises a pair of catching arms provided substantially in parallel with, and outside of, the periphery of the position limiting device, where an opening is provided between the pair of catching arms for catching the pickup line between the catching arms and the periphery of the position limiting device.
• the opening between the pair of catching arms is provided with a locking device for preventing the pickup line from exiting from the catching device through the opening.
• the catching arms are pivotally fastened to a peripherical member of the position limiting device.
• the catching arms are pretensioned by means of a spring device.
• the catching device comprises substantially T-shaped catching elements protruding from the position limiting device.
• the position limiting device is substantially circular.
• Fig. 1 illustrates a side view of a prior art system for transferring load from a sub sea storage device to the sea surface
• Fig. 2 illustrates a side view of that prior art system
• Figs. 3, 3a and 3b illustrate a side view of a system according to one embodiment of the invention in place
• Fig. 4a illustrates a pickup line zone of the prior art system in fig. 1.
• Fig. 4b illustrates the pickup line zone of the system in fig. 3.
• Fig. 5 illustrates details of the embodiment in fig. 3.
• Fig. 6 illustrates a perspective view of the position limiting device of fig. 5.
• Fig. 7 illustrates an embodiment of the catching device of the position limiting device shown in fig. 6.
• Fig. 8 illustrates an alternative embodiment of the catching device, and.
• Figs 9a to 9d show variants of a component of the catching device.
• an active transfer device comprising gooseneck 13 and loading riser 10 is provided in the top of the tension buoy 14.
• the element of the transfer device may be a flexible hose/riser 10, which is hanging freely down from the tension buoy 14 when not in use. Since the tension buoy 14 and the loading riser 10 are submerged in the sea, they will not be damaged by vessels on the surface 5 or during bad weather conditions.
• a pickup line 11, 11a, l ib is used for picking up the loading riser 10 from sea when load is to be transferred from the tension buoy 14 to the vessel 2 on the sea surface 5.
• the pickup line 11 is connected to the loading riser 10 at its end away from the tension buoy 14.
• the pickup line 1 1 leads to a spring buoy 15.
• the spring buoy 15 is connected to an intermediate pick up line 1 la, a master link 16 and an upper pickup line l ib terminated in the marker buoy 17 available at the sea surface.
• One or several marker buoys 17 can be provided in the second end of the upper pickup line l ib for easy access from the vessel.
• the system comprises a swivel device 20 for connection of the loading riser 10 to the tension buoy 14.
• the swivel device 20 ensures that fluid communication with the tension buoy 14 is possible for the different positions that the tanker 2 may have in relation to the tension buoy 14.
• the swivel device 20 would be familiar for a person skilled in the art. More details of the swivel device are shown in fig. 5.
• the vertical swiveling device 20 may be located under the tension buoy 14.
• the tension buoy 14 may be oriented according to the weather conditions together with the loading riser 10 and the pickup line 1 1.
• the "catching wheel” is suited to work equally well for all alternatives.
• the system further comprises a horizontal swiveling device for rotation of the loading riser 10 and the pickup line 11 in relation to the tension buoy 14.
• the loading riser 10 and the pickup line 11 will then orient themselves according to the influence of weather conditions, such as waves/currents in the sea.
• the system further comprises a position limiting device 21 fixed to the swivel 20, for limiting the position of the pickup line 1 1 in relation to the tension buoy 14.
• the position limiting device 21 may be located above the gooseneck connection device 13. This will be explained more in detail with reference to figs. 4a and 4b.
• area A illustrates the different positions the pickup line 1 1 may have in relation to the tension buoy 14, as viewed from above in a coordinate system which rotates with the vertical swivel.
• the borderline is calculated in such a way, that the swivel will start to swivel for a sea current which is also strong enough to pull the pick up line over the edge of the area A.
• the borderline curve is referred to as the pick up line envelope.
• the position limiting device 21 intersects the periphery of the area A and divides the area into three parts.
• the pick up line can obviously no longer transit inside the position limiting device 21, indicated by area C. But it is also prevented from transiting around the limiting device for reasons described above.
• area B is also off limits, provided the tanker drops the line in the direction of area A, (which it always does as described earlier).
• the position limiting device 21 limits the possible positions for the pickup line 11. So since area C is excluded, the pickup line will not get entangled by any of the details on the swivel 13 or the tension buoy 14. Since area B is also excluded, the pickup line will not get wrapped around the tension buoy 14 or the rigid riser 4. This is precisely what the invention aimed to achieve.
• the position limiting device 21 is shown in more detail.
• the position limiting device 21 may be substantially circular, as indicated in fig. 9a, for example provided as a wheel with spokes or alternatively as a substantially circular plate device.
• the position limiting device 21 may have other shapes as well, such as a substantially semi-circular shape as shown in fig. 9b and 9c, or a substantially curved form, where the outer periphery of the curve faces towards area A as in fig. 5.
• the position limiting device 21 is a fabricated wheel structure, comprising a hub 22 in the rotation centre, spokes 23 extending radially from the hub 22 to a peripheral member 24, which in this embodiment is a wheel.
• the hub 22 is fixed to the connection device 13, i.e. rotation of the peripheral member 24 is performed by means of the position limiting device 21.
• the position limiting device 21 may also include buoyancy elements. Such buoyancy elements are secondary to the invention, but may be preferred in some cases.
• the position limiting device 21 may include a catching device 30 for catching and holding the pickup line 11.
• the catching device 30 may be provided on the periphery of the wheel 24.
• the catching device 30 comprises a pair of catching arms 31a, 31b provided substantially in parallel with, and outside of, the periphery of the position limiting device 21.
• the periphery of the position limiting device 21 is similar to the periphery of the wheel 24.
• An opening 32 is provided between the pair of catching arms 31a, 31b for catching the pickup line between the catching arms 31a, 31b and the periphery of the position limiting device 21.
• the pickup line 11 when the pickup line 11 moves to a position near the periphery of the position limiting device 21 , the pickup line 11 will slide along it, and it will enter the opening 32. In this situation, the pickup line 11 will be caught between one of the catching arms 31a, 31b and the periphery of the position limiting device 21 or wheel 24.
• the opening 32 between the pair of catching arms 31a, 31b may be provided with a locking device 33 for preventing the pickup line from exiting from the catching device 30 through the opening 32.
• the locking device 33 may comprise a curved plate fixed to each end of the catching arm near the opening 32, where each curved plate protrudes into the area between the periphery of the wheel 24 and the catching arm. In this way, the curved plates may guide the pickup line through the opening 32, while the plates prevent the pickup line 11 from exiting through the opening 32.
• Several such pairs of catching arms are provided along the periphery of the position limiting device 21/the periphery of the wheel 24.
• a space 34 between each pair of catching arms may have a cover (not shown) to guide the pickup line 11 further to the nearest opening 32.
• Each catching arm 31a, 31b may be pivotally fastened to the peripheral member of wheel 24 of the position limiting device 21, for example by means of a pivot axle or fastening pin 35.
• Each catching arm is pretensioned and is held in its initial position as shown in fig. 7.
• the catching arms may be pretensioned by means of a spring device (not shown).
• the catching device 30 includes a releasing mechanism for releasing the pickup line 1 1 from the catching device.
• the releasing mechanism is provided for release of the pickup line 11 when a traction force in the pickup line 11 reaches a predetermined limit.
• the predetermined limit is set such that the releasing mechanism does not activate because of sea currents etc, but only if a tanker starts to pull in the pick up line.
• the vessel is not located above the tension buoy, but is located for example 20 - 60 meters from the tension buoy 14 - see fig 3c. Hence, the traction force from the vessel has a considerable horizontal component.
• the catching device 30 comprises substantially T-shaped catching elements 39 protruding radially from the periphery of the position limiting device 21.
• the pickup line 11 when the pickup line 11 moves to a position near the periphery of the position limiting device 21, the pickup line 11 will slide along it, and it will be caught by the T-shaped catching elements 39. This will prevent the pick up line from sliding any further along the wheel circumference. But whenever the current changes direction, the pick up line may slip out of the T shaped catch and it will re- enter area A of the pick up line envelope as shown in figure 4b. As we have seen earlier the line may stay indefinitely in this area without causing any problems, but it will of course re-enter the T-catch 39 regularly.
• the position limiting device 21 together with the gooseneck connection device 13 will rotate around the rotation axis of the swiveling device, until the T-shaped catching element 39 is at an attitude where it releases the pickup line again along the slanted surface under the T.
• the position limiting device keeps the pick up line away from the complex details on top of the tension buoy. Hence entanglement is eliminated.
• the critical diameter or circumferential size of the position limiting device is large enough to prevent the currents from taking the pick up system around the position limiting device.
• the selected diameter is above this value. Hence wrapping of the rigid riser is eliminated.
• the present invention is mainly active during the standby period.
• Figure 3a shows the loading system with the position limiting device 21 installed in the stand by phase.
• Figure 3b shows the situation during loading. As seen, the position limiting device 21 does not affect the loading operation, and makes a significant difference operationally during the pick up operation.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• Ocean & Marine Engineering (AREA)
• Earth Drilling (AREA)
• Jib Cranes (AREA)
• Ship Loading And Unloading (AREA)

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• 2011
  • 2011-02-02 EP EP11706040.0A patent/EP2531399B1/de not_active Not-in-force
  • 2011-02-02 BR BR112012019331A patent/BR112012019331A2/pt not_active IP Right Cessation
  • 2011-02-02 WO PCT/NO2011/000040 patent/WO2011096819A2/en not_active Ceased
  • 2011-02-02 AU AU2011213355A patent/AU2011213355B2/en not_active Ceased
  • 2011-02-02 US US13/574,619 patent/US8944871B2/en active Active
  • 2011-02-02 CN CN201180008000.0A patent/CN102869567B/zh not_active Expired - Fee Related

Non-Patent Citations (1)

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